We describe survey results from a representative sample of 1,075 U. S. social network users who use Facebook as their primary network. Our results show a strong association between low engagement and privacy concern. Specifically, users who report concerns around sharing control, comprehension of sharing practices or general Facebook privacy concern, also report consistently less time spent as well as less (self-reported) posting, commenting and "Like"ing of content. The limited evidence of other significant differences between engaged users and others suggests that privacy-related concerns may be an important gate to engagement. Indeed, privacy concern and network size are the only malleable attributes that we find to have significant association with engagement. We manually categorize the privacy concerns finding that many are nonspecific and not associated with negative personal experiences. Finally, we identify some education and utility issues associated with low social network activity, suggesting avenues for increasing engagement amongst current users.

The strong emotional reaction elicited by privacy issues is well documented (e.g., [12, 8]). The emotional aspect of privacy makes it difficult to evaluate privacy concern, and directly asking about a privacy issue may result in an emotional reaction and a biased response. This effect may be partly responsible for the dramatic privacy concern ratings coming from recent surveys, ratings that often seem to be at odds with user behavior. In this paper we propose indirect techniques for measuring content privacy concerns through surveys, thus hopefully diminishing any emotional response. We present a design for indirect surveys and test the design's use as (1) a means to measure relative privacy concerns across content types, (2) a tool for predicting unwillingness to share content (a possible indicator of privacy concern), and (3) a gauge for two underlying dimensions of privacy -- content importance and the willingness to share content. Our evaluation consists of 3 surveys, taken by 200 users each, in which privacy is never asked about directly, but privacy warnings are issued with increasing escalation in the instructions and individual question-wording. We demonstrate that this escalation results in statistically and practically significant differences in responses to individual questions. In addition, we compare results against a direct privacy survey and show that rankings of privacy concerns are increasingly preserved as privacy language increases in the indirect surveys, thus indicating our mapping of the indirect questions to privacy ratings is accurately reflecting privacy concerns.

For privacy reasons, sensitive content may be revised before it is released. The revision often consists of redaction, that is, the "blacking out" of sensitive words and phrases. Redaction has the side effect of reducing the utility of the content, often so much that the content is no longer useful. Consequently, government agencies and others are increasingly exploring the revision of sensitive content as an alternative to redaction that preserves more content utility. We call this practice sanitization. In a sanitized document, names might be replaced with pseudonyms and sensitive attributes might be replaced with hypernyms. Sanitization adds to redaction the challenge of determining what words and phrases reduce the sensitivity of content. We have designed and developed a tool to assist users in sanitizing sensitive content. Our tool leverages the Web to automatically identify sensitive words and phrases and quickly evaluates revisions for sensitivity. The tool, however, does not identify all sensitive terms and mistakenly marks some innocuous terms as sensitive. This is unavoidable because of the difficulty of the underlying inference problem and is the main reason we have designed a sanitization assistant as opposed to a fully-automated tool. We have conducted a small study of our tool in which users sanitize biographies of celebrities to hide the celebrity's identity both both with and without our tool. The user study suggests that while the tool is very valuable in encouraging users to preserve content utility and can preserve privacy, this usefulness and apparent authoritativeness may lead to a "slippery slope" in which users neglect their own judgment in favor of the tool's.